Hydroforming process with pretreatment of recycle gas



April 14, 1959 M. A. EFROYMSON HYDROFORMING PROCESS WITH PRETREATMENT OF RECYCLE GAS F iled Oct. 5, 1953 lli ll 8 7 I 6 FEED OIL H2 r0 START Meyer 4. E froymsbn Inventor By Attorney United States *Patent O HYDROFORMING PROCESS WITH PRETREAT- MENT OF RECYCLE GAS Meyer A. Efroymson, Elizabeth, NJ., assignor to Esso Research and Engineering Company, a corporation of Delaware Application October 5, 1953, Serial No. 384,069

6 Claims. (Cl. 208-62) This invention relates to improvements in the hydroforming of naphthas. More particularly it relates to a hydroforming process utilizing platinum type catalysts wherein undesirable degradation of the catalysts by coking is prevented through pretreatment of the recycle gas.

Hydroforming is defined as an operation in which a petroleum naphtha is contacted at elevated temperatures and pressures and in the presence of a recycled hydrogencontaining gas with a solid catalytic material under conditions such that there is no net consumption of hydrogen.

Usually the feed stock boils substantially within the range of from about 150-430 F. and more particularly 200-350 F. The light ends, i.e., the material boiling from about O-200 F., are not usually subjected to this reaction, for the reason that the virgin naphtha light ends have a fairly good octane rating. The feed or charging stock to the hydroforming reactor can be a virgin naphtha, a cracked naphtha, a Fischer-Tropsch naphtha, a mixture of these, or the like. The process of this invention is particularly suited for the hydroforming of virgin naphtha.

Hydroforming operations are ordinarily carried out in the presence of hydrogen or hydrogen-rich recycle gas at temperatures of 800-l000, F., in the pressure range of about 50 to 750 pounds per square inch, and in contact with hydroforming catalysts.

The chemical reactions involved in the hydroforming process include dehydrogenation of naphthenes to the corresponding aromatics, isomerization of straight chain paraflins to form branched chain paraflins, isomerization of cyclic compounds such as ethylcyclopentane to form methylcyclohexane, and some aromatization, dealkylation and hydrocracking of paraffins. In a hydroforming operation which is conducted efiiciently it is possible with the use of a proper catalyst and proper conditions of operation to hydroform a virgin naphtha having an octane number of about 50 to a hydroformate having an octane number of from 95 to 98 and obtain yields of hydrocarbons as high as 85%. The hydroforming can be carried out either by the fixed bed process or in accordance with the fluidized solid technique.

One of the main problems in carrying out a hydroforming operation is that of supplying heat to support the highly endothermic reaction. That explains the utilization in fixed bed systems of 2 or 3 reactors for best results and the increased utilization of the one vessel fluidized, isothermal technique in order to get the requisite severity of operation. One way of supplying the heat is by heating the hydrogen-containing gas to a temperature of 1000-l200 F. This temperature can cause cracking of hydrocarbons, which comprise to 50% of the recycle stream. For example, a typical recycle gas from the reice cycle gas preheater with a coil outlet temperature of 1200" F. contains 0.8 to 0.9 mol percent propylene and 0.4 to 0.5 mol percent butylenes. Since a hydroforming process operates in the range of 3/1 to 10/1 moles of recycle gas per mole of naphtha feed, these small percentages of olefins in the recycle are equivalent to 5-15 mol percent unsaturation in the feed itself. Numerous investigations have shown that unsaturated hydrocarbons cause deactivation of hydroforming catalysts. Consequently, it is apparent that a sizable decrease in catalyst activity and selectivity degradation can be caused by poisoning and coking due to these unsaturates in the recycle gas. The carbonized materials on the catalyst reduce selectivity and activity. While they can be removed easily by regeneration with oxidizing gas, e.g., air in the case of group VI metal oxide catalysts such as M0 0 it is quite often not desirable to subject platinum type catalysts to this regeneration treatment.

This invention provides an improved process for preventing catalyst degradation due to the presence of olefins in the heated recycle gas. The process comprises pretreat ing the heated recycle gas containing low molecular weight unsaturated hydrocarbons, principally in the C to C range, with a hydrogenation catalyst prior to the utilization of the recycle gas in the reactor. This hydrogenation catalyst present in a guard catalyst chamber results in the hydrogenation, polymerization and decomposition of the olefins present in the gas at the temperature of 1000-1200 F. The coke produced by polymerization and decomposition is deposited on the guard catalyst, and not on the catalyst within the reactor. This coke deposition is therefore made on a catalyst which can be discarded or is much more amenable to regeneration for economic and other reasons. The time between platinum hydroforming catalyst replacement or regeneration can therefore be extended considerably, i.e., to a cycle of several months or longer. This utilization of a guard chamber to pretreat the recycle gas at elevated temperatures is thus used for a completely difierent purpose than guard chambers on fresh feed at lower temperatures.

This invention will be better understood by reference to the flow diagram shown in the drawing illustrating the use of the invention in a single reactor hydroformer. It will be understood, of course, that more than one reactor can be employed, e.g., 2 or 3. The guard chamber is not needed between reactors because of the high hydrogen partial pressure.

In the drawing, 1 represents a reactor containing a bed C of catalyst, the active component of which catalyst is a platinum group metal, such as platinum itself, carried on a suitable support such as active alumina. In the operation, hydrogen-containing recycle gas recovered from the crude product is withdrawn from a separator S via line 10, then passed through compresser 11 into line 12, from which it is charged to a furnace 13, heated in coil 14, withdrawn and charged via 15 into guard chamber 50 containing hydrogenation catalyst 52. The olefins are hydrogenated and thus sent along with the residual recycle gas stream through line 51 into reactor 1. The hydrogenation catalyst also polymerizes and cracks some of the olefins to coke and carbon, which are then deposited on the hydrogenation catalyst itself.

The hydrogen-containing gas enters the bottom of the reactor, passes upwardly through grid G and into the bed C of catalyst.

The oil to be treated, which would ordinarily be a virgin naphtha containing from 30-45% of naphthenes, is introduced in the present system through line 16, is thereafter heated in coil 17 in furnace 13 to a temperature of around 950 F., thereafter withdrawn from the furnace 13 through line 18, and charged into the bed of catalyst above the grid G, but in relatively close proximity thereto.

Under conditions more fully set forth hereinafter, the desired conversion takes place, the principal chemical reaction being one in which naphthenes are dehydrogenated to the corresponding aromatic, as where methylcyclohexane is dehydrogenated to form toluene. The vapors and gases emerge from the reactor via line 21 to a cooler 22 wherein the normally liquid constituents are condensed and thereafter charged via line 23 into the separator S. The crude product is withdrawn from separator S via line 24 and delivered to product purification in equipment not shown while the hydrogen-containing gas is recovered via line 10, as indicated above.

In order to explain the invention more fully, the following conditions of operation of the various components are set forth below and in the examples.

Conditions in reactor 1 Preferred Range Catalyst composition, wt. percent platinum on activated alumina; 0. 0. 1-2 Temperature, F 800-1. 000 700-1, 000 Pressure, p.s.i.g 150-250 50-750 V.[V,./Hr. (Vol. oil/Vol. cat./Hr.) 1. 0-4. 0 0. 2-10 Cu. it. of recycled gas fed/bbl. of oil 2, 500-7, 000 1, 000-10, 000 Concentration of Hz in recycle gas 65-80 50-95 Conditions in guard chamber 50 Preferred Range Temperature of treatment, F.-- 1, 000-1, 200 900-1, 400 Pressure, p.s.i.g 150-250 50-750 Residence time, seconds 2.0 to 5.0 .5 to Hydrogenation catalyst to hydroforming catalyst ratio .2 to .4 .1 to 1.0

The range of olefins that can be found in the recycle gas entering the guard chamber is 0.1 to 2.0 weight percent.

In the hydroforming process itself the feed stock is preheated to the maximum temperature possible while avoiding excessive thermal degradation of the feed stock. Ordinarily preheating of the feed stock is carried out to temperatures of about 8001050 F., preferably about 900-950 F. The naphtha preheat should be as high as possible while avoiding thermal degradation thereof as by limiting the time of residence in the transfer or feed inlet lines. The preheated feed stock may be supplied to the reaction vessel in admixture with hydrogenr'ich recycle gas or it may be introduced separately as shown. The recycle gas, which contains from about 65 to 80 volume percent hydrogen, is preheated to temperatures of about 1000"-l200 F., preferably about 1050 F., prior to the introduction thereof into inlet line 15. After the heated recycle gas passes through the guard chamber 50, it may be supplied to the reaction vessel in admixture with the preheated feed stock or may be introduced separately as shown. The recycle gas should be circulated through the reactor at a rate of from about 2000 to 8000 cubic feet per barrel of naphtha feed. The amount of recycle gas. added is preferably the minimum amount that will suflice to carry the necessary heat of reaction into the reaction zone and keep the carbon formation at a satisfactory low level.

The process of this invention is applicable to fixed or fluid bed hydroforming. Suitable hydroforming catalysts are the noble metal catalysts such as platinum, palladium, gold, silver, iridium, rhodium, ruthenium, osmium, etc. These noble metals are generally associated and 4 supported on a metal oxide and particularly an oxide of a metal in the left hand columns of groups III to VIII of the periodic table, including particularly the oxides of silicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium, tantalum, chromium, tungsten, uranium, manganese, etc. It is understood that the catalyst can comprise two or more noble metals and the base two or more metal oxides. In still other cases, one or more activating components may be included in the catalyst. Particularly suitable is the platinum on alumina catalyst, which is normally present on the alumina in an amount of from 0.1 to 2 weight percent. The catalyst particles can be pills, powders, pellets, or other form known in the art. Catalyst particles are for the most part between from 200 to 400 mesh in size or about 10 to 200 microns in diameter, with a major portion between 20 and microns in fluidized operation.

While the process of this invention is also applicable to the prevention of degradation of other hydroforming catalysts, i.e., molybdena, chromia, etc., its greatest utility is as disclosed above.

The hydrogenation catalysts or guard catalysts can be used in the conventional physical form in which they are available such as pills, pellets, powder, etc. Two or more guard chambers can be utilized so that one could be shut down while the other is working.

Various types of hydroforming and hydrogenation catalysts can be used as the guard catalyst, including molybdena, chromia, copper chromia, iron, nickel, tungsten, and tungsten nickel sulfide catalysts. The spent hydroforming catalyst itself can also be used as the guard catalyst, since it will have adequate hydrogenation activity for this purpose even after it is no longer economically satisfactory as a hydroforming catalyst.

Particularly preferred is the spent platinum hydroforming catalyst itself.

When molybdena is used as the guard catalyst, the effluent also should be contacted with alumina to prevent the volatile molybdenum metal from going through to the reactor and poisoning the platinum catalyst.

The advantages of the process of this invention are apparent to the skilled in the art. Great savings result because less expensive, more readily available catalysts are subjected to coking rather than taking this loss in the reactor itself. An improved process results because of the increased life and better activity and selectivity of the hydroforming catalyst. Other advantages will be apparent.

It is to be understood that this invention is not limited to the specific examples, which have been offered merely as illustrations, and that modifications may be made without departing from the spirit of this invention.

What is claimed is:

1. In a process for hydroforming hydrocarbons utilizing a supported platinum hydroforming catalyst wherein olefins in the hydrogen-containing recycle gas are normally introduced into the main reaction zone and consequently result in hydroforming catalyst degradation, the improvement which comprises heating the olefin-containing recycle gas to temperatures of 900 to 1400 F., contacting the entire stream of preheated recycle gas with a separate hydrogenation catalyst not used in the hydroforming of the hydrocarbons thereby eliminating olefinic materials from the recycle gas and preventing the degradation of the hydroforming catalyst.

2. The process of claim 1 in which the hydrocarbon being hydroformed is a virgin petroleum naphtha.

3. The process of claim 2 in which the hydroforming catalyst is platinum on activated alumina.

4. The process of claim 3 in which the olefins present in the recycle gas sent to pretreatment are predominantly in the C to C range and the pretreatment is conducted at a temperature in the range of 1000-1200 F.

' '5. The process of claim 4 in which the hydrogenation catalyst is a molybdena catalyst.

6. The process of claim 4 in which the hydrogenation 2,479,109 catalyst is a spent platinum catalyst. 2,656,304 2,737,476 References Cited in the file of this patent 2,753,052

UNITED STATES PATENTS 5 1,812,526 Gross et a1. June 30, 1931 2,131,806 Ipatiefi et a]. Oct. 4, 1938 2,374,109 Layng et a1 Apr. 17, 1945 2,472,844 Munday et a1 June 14, 1949 6 Haensel Aug. 16, 1949 McPhersonet a1 Oct. 20, 1953 Hardy et a1. Mar. 6, 1956 Arundale et al Aug. 7, 1956 OTHER REFERENCES Reactions of Pure Hydrocarbons, Eglofi", page 105, Reinhold Publishing Corp., New York (1939).

Progress in Petroleum Technology, page 45, Table III, Amer. Chem. 800., Washington, DC. (Aug. 7, 1951). 

1. IN A PROCESS FOR HYDROFORMING HYDROCARBONS UTILIZING A SUPPORTED PLATINUM HYDROFORMING CATALYST WHEREIN OLEFINS IN THE HYDROGEN-CONTAINING RECYCLE GAS ARE NORMALLY INTRODUCED INTO THE MAIN REACTION ZONE AND CONSEQUENTLY RESULT IN HYDROFORMING CATALYST DEGRADATION, THE IMPROVEMENT WHICH COMPRISES HEATING THE OLEFIN-CONTAINING RECYCLE GAS TO TEMPERATURES OF 900* TO 1400* F., CONTACTING THE ENTIRE STREAM OF PREHEATED RECYCLE GAS WITH A SEPARATE HYDROGENATION CATALYST NOT USED IN THE HYDROFORMING OF THE HYDROCARBONS THEREBY ELIMINATING OLEFINIC MATERIALS FROM THE RECYCLE GAS AND PREVENTING THE DEGRADATION OF THE HYDROFORMING CATALYST. 